A liquid crystal display device is one example of display devices that are used as high-definition color monitors for computers and other information devices, and as television receivers. A liquid crystal display device fundamentally includes a display portion in which liquid crystals are sandwiched between two substrates at least one of which is made of transparent glass or the like. In addition, a liquid crystal display device includes a driver for selectively applying voltages to pixel electrodes formed on the substrate of the display portion. Pixels of the respective pixel electrodes are controlled based on the voltage applied by the driver.
The display portion generally includes gate signal lines, source signal lines, and pixel electrodes. The gate signal lines, for example, respectively extend in a horizontal direction (main scanning direction), and are aligned in a vertical direction (sub scanning direction). The source signal lines, for example, respectively extend in the vertical direction (sub scanning direction), and are aligned in the horizontal direction (main scanning direction). Thin film transistors (TFTs) and the pixel electrodes are disposed in a matrix at intersection points of the gate signal lines and the source signal lines. A gate driver outputs voltages (gate signals) to the gate signal lines for turning the TFTs on and off. A source driver outputs voltages (source signals) based on an input image signal to the pixel electrodes via the source signal lines to thereby control transmittance of liquid crystals provided corresponding to the pixel electrodes to values according to the source signals.
A display device smoothly displays images on a display portion by successively switching frame images to be displayed on the display portion, for example, based on image signals input from outside. A framefrequency, a frequency of switching a frame image is generally 60 Hz. A display device is conventionally known to detect whether an input image signal is a signal representing still picture or moving picture, and switch the framefrequency depending on a result of detection, for example, described in a prior art (See Japanese Unexamined Patent Application Publication No. JP 2003-280578). This prior art discloses a display device which detects whether an image signal is a still picture or a moving picture, and switches to lower the framefrequency when it detects a still picture. It can decrease power consumption when the display device displays an image.
The display device according to the prior art, however, does not lower the frame frequency, in a case that even if an input image signal represents a still picture in a part of an image, it represents a moving picture in the other part of an image. Therefore, there is a problem in that it does not reduce power consumption enough.